Chlamydias are gram-negative bacteria, obligate intracellular parasites of eukariotic cells. Chlamydias show an extracellular infective and metabolically practically inert form, called elemental body (EB), and intracellular replicative forms called reticular bodies (RB).
The reticular bodies, after multiplication by binary fission, are transformed into elemental bodies which come out of the host cell and infect new cells.
The masses or mini-colonies of reticular and elemtal bodies inside an infected cell constitute the characteristic "inclusions" visible at the optical microscope.
Chlamydia trachomatis (C. trachomatis or CT), a bacterial species pathogenic to man, is the etiological agent of venereal lymphogranuloma (VLG), of various inflammatory patologies of the genital male and female apparatus and of trachoma, a chronic disease which affects 500 million people and can lead to blindness.
In the technical literature ca. 15 CT serotypes pathogenic to man were described and divided in two groups which differ both as to virulence and tissular tropism.
Twelve serotypes of the trachoma group (biovar) are identified as A to K and infect, in general, epithelial tissues, such as the ocular (trachoma) and uro-genital (cervicitis and urethritis) mucous membranes, and show a low virulence.
The venereal lymphogranuloma (VLG) serotypes (L.sub.1, L.sub.2 and L.sub.3) cause instead an infection of the reticulo-endothelial tissue, mainly of the inguinal and femoral lymphonodi, and are highly invasive.
Urethritis and cervicitis induced by CT (A to K serotypes) when not precociously diagnosed and treated by adequate therapy, may led to a variety of chronic inflammations, such as, e.g., vaginitis, salpingities and pelvic inflammation which may resolve in sterility and extrauterine pregnancy.
Furthermore the new born from infected mothers may contract pulmonary and/or ocular infections during delivery.
For said reason it is necessary to possess adequate diagnostic methods for determining CT and formulating effective vaccines against said bacterium.
As known, factors which determine the bacterial virulence are often encoded by genes present on plasmids.
In the literature, the presence is reported, in all 15 serotypes and in the clinical isolates examined up to now, of a plasmid of ca. 7.5 Kb referred to in the present invention as pCT followed by the denomination of the bacterial serotype concerned. For example: pCTD for the plasmid isolated from serotype D, etc.
Up to now, however, no specific function or products encoded by it were associated with said plasmid.